Rotary pump



Aug. 31, 1965 M. PURCELL 3,203,355

ROTARY PUMP Original Filed May 3, 1960 3 Sheets-Sheet 1 LNVENTOR HOWARDM.PURCELL ATTORNEY Aug. 31, 1965 H. M. PURCELL. 3,203,355

ROTARY PUMP Original Filed May 3, 1960 3 Sheets-Sheet .2

INVENTOR.

HOWARD M. PURCELL N s' k WWW ATTORNEY United States Patent 3,203,355R'OTARY PUMP Howard M. Purcell, Cleveland, Ohio, assignor to Parker-Hannifin Corporation, Cleveland, Ohio, a corporation of OhioContinuation of application Ser. No. 26,646, May '3, 1960.

This application July 24, 1963, Ser. No. 299,138 18 Claims. (Cl.103-126) This application is a continuation of my copending applicationSerial No. 26,646, filed May 3, 1960, and entitled Rotary Pump, thisapplication now being abandoned.

This invention relates to rotary pumps or motors and more particularlyto those of the type having a pressure loaded element for sealing theside faces of the rotary member.

In pumps of the type referred to above, as for example, in gear pumps,the rotary members have teeth with spaces or pocket areas therebetweenwhich become filled with liquid under low pressure as the pocket areaspass the pump inlet and which discharge the fluid under high pressureinto the pump outlet. The side openings of such pockets are closed bywear plates or bushings. Fluid in pockets which are exposed to theoutlet is under pressure and reacts against such wear plates or bushingstending to separate the same from the gear side faces and thus permitleakage of fluid from high pressure areas to areas of low pressurewhich, if permitted, results in low volumetric efliciency and is thusundesirable. To prevent such separation and leakage, the wear plates orbushings are pressed by means of fluid pressure into sealing engagementwith the side faces of the gear teeth, fluid under pressure for thispurpose being diverted from the pump outlet and applied against pistonsor the like movable by such fluid pressure.

Since the wear plates or bushings are non-rotatable, there is runningfriction between the same and the gear side faces as the gears rotate,such running friction causing loss of mechanical efliciency and creatingundesirable heat. To minimize these adverse characteristics, it isdesirable to maintain only the minimum amount of pressure between thewear plates and gear side faces to assure satisfactory sealing.

The construction of the pump parts may be such that during rotation ofthe gears the total area of any wear plate subject to high pressuretending to move the wear .plate away from the gear may rapidlyfluctuate, and hence the total separating force on the wear plate willlikewise rapidly fluctuate. It is an object of the present invention toeffectively resist such fluctuating forces without applying unduecounterforce to the wear plates which would otherwise cause excessiveheat and loss of mechanical efliciency.

It is another object to provide a counterforce which increases anddecreases as the total separating force increases and decreases so thata substantially uniform differential between the two'forces ismaintained, such differential force being suflicient to maintain thewear plate in sealing contact with the rotor without excessive friction.

It is another object to utilize a portion of the fluid from the pumpoutlet for generating the counterforce described and to trap such fluidportion in a manner so that its pressure will increase and decrease asthe fluctuating separating forces on the wear plates increase anddecrease but wherein there will be a gradual reduction of the pressureof the trapped fluid whenever its pressure exceeds the pressure of fluidinthe pump outlet for a period of time longer than the cycle time of thefluctuating forces.

Patented Aug. 31, 1965 "ice Other objects will be apparent from thefollowing description and from the drawings in which:

FIGURE 1 is a longitudinal section through the lines 1-1 of FIGURE 3,

FIGURE 2 is a section through lines 2-2 of FIG- URE 3,

FIGURE 3 is a section, partially fragmentary, through the lines 3-3 ofFIGURE 1, and

FIGURE 4 is a fragmentary enlarged section view along the lines 4--4 ofFIGURE 1.

In the example disclosure of embodiment of the invention the pumpstructure includes a body 10 and end closures 11 and 12 secured to thebody by screws 13. O-ring seals 14 may be provided between the endclosures 11 and 12 and the body 10. The end closure 11 is formed with ahollow boss 15 containing suitable bearings for the drive shaft 16 and acap plate 17 is secured to the boss and contains a suitable seal for theouter end of said shaft. The inner end of the shaft 16 has externalspline ribs 18 for engagement with one of the meshed pumping gears to bedescribed hereinafter.

The body 10 includes a chamber comprising two longitudinal cylindricalbores 19 and 19a which intersect at a median plane P (FIGURES 1 and 3).In FIGURE 3 a second plane P has been indicated extending diametricallythrough the longitudinal centers of the bores 19 and 19a. At one side ofthe plane P the body 10 has an internal recess 20 which opens throughthe walls of the bores 19 and 19a and provides a receiving zone R forthe fluid to be pumped. At the opposite side of the plane P the body 10has another recess 21 which opens through the walls of the bores 19 and19a and Provides a delivery zone D to which the pumping gears deliverthe fluid from the receiving zone R. The zone R has an inlet 22 forconnection with a fluid inlet conduit and the zone D has an outlet 23for connection with a fluid delivery conduit.

One set of bearing blocks or bushings (FIGURE 1) 24 and 24a is providedat one end of the body 10 and a second set of bearing blocks orbushings'25 and 25a is provided at the other end of said body. Theblocks 24 and 25 are in the ends of the bore 19 and conform thereto, andthe blocks 24a and 25a are in the ends of the bore 19a and conformthereto. The blocks 24 and 24a of the first set solidly abut the endclosure 11, and the blocks 25 and 25a are adjacent to but spacedinwardly from the inner side of the end closure 12. The closure 11 ispreferably recessed somewhat at 26 (FIGURE 1) to receive the outer endsof the blocks 24 and 24a. These blocks 24 and 24a have flat surfaces 27which abut at the median plane P, and the blocks 25 and 25a also haveflat surfaces 28 which abut at said plane P. All of the blocks orbushings 24, 24a, 25 and 25a are identical for ease of manufacture andassembly, and suitable sealing means 29 is provided for sealing againstfluid egress endwise outwardly about the blocks or between the abuttingflat faces 27 and 28 of the block sets.

A plurality of movable elements or wear plates 30 and 30a, of a firstset, contact with the inner sides of the bearing blocks 24 and 24a,respectively, and have straight edges 31 which abut at the median planeP. Other movable elements or wear plates 32 and 32a, of a second set,contact with the inner sides of the bearing blocks 25 and 25arespectively,and have straight edges 33 which abut at the median planeP. All of the wear plates 30, 30a, 32 and 32a peripherally conform tothe bores 19 and 19a except in the region of the fluid receiving zone R.In this region, said wear plates are notched at 34 (FIGURE 3) to allowend filling as well as radial filling of a plurality of tooth pocketareas of the pumping gears with fluid entering at the inlet 22.

As viewed in FIGURES l and 3, each of the wear plates 30, 30a, 32 and32a has a central opening 35, and first means comprising an arcuategroove 36 concentric with said opening 35 and including a groove 37leading from said arcuate groove 36 through the peripheral edge of theplate. Both grooves 36 and 37 are open to the inner side faces of therespective wear plates. Each groove 36 extends from a point 36a (FIGURE3) about midway between the receiving zone R and the delivery zone D toa point 36b in the zone in which the rotary pumping gears mesh, and eachradial groove 37 is in direct communication with the delivery zone D.The purpose of the grooves 36, 37 will be described in detailhereinafter.

A rotary member or pumping gear 38 is interposed between the two movablewear plates 30 and 32 and has its side faces in sealing contact with theinner side faces of said wear plates. Another rotary member or pumpinggear 38a is interposed between the two wear plates 30a and 32a and hasits side faces in sealing contact with the inner faces of these wearplates. The two gears mesh across the median plane P as seen in FIGURE 3and their teeth radially span the wear plate grooves 36.

Each gear 38, 38a has tubular bearing stubs 39 extending through thewear plate openings 35 mounted in roller bearings 40 within the bearingblocks 24, 24a, 25 and 25a. Each gear has internal spline ribs 41. Thespline ribs 41 of the gear 38 engage with the external spline ribs 18 ofthe drive shaft 16. The gear 38a is driven by the drive shaft 16 throughthe gear 38, as is best illustrated in FIGURES 1 and 3.

The first means or wear plate grooves 36 and 37 serve to communicate thepressure existing in outlet recess D to approximately half of theplurality of tooth pocket areas in each gear and also serve to relievefluid which would otherwise be trapped in the plurality of tooth pocketareas in the gear meshing zone. Such relief is desirable because as theteeth mesh, the pocket area portion occupied by fluid progressivelydecreases until the pocket area is centered on median plane P, afterwhich it increases. Without the relief, the fluid trapped in suchdecreasing pocket area portions is forced to compress and developsextremely high pressures which are detrimental to the pump.

The fluid under pressure in the plurality of tooth pocket areasconnected by the grooves 36 acts on the adjacent area of the inner facesof the wear plates 30, 30a, and 32, 32a, tending to separate the wearplates from the gear side faces, which would result in leakage of fluidfrom the high pressure zone D to the low pressure zone R. Fluid in thetooth pocket areas toward the low pressure cavity R is under lowpressure and therefore exerts no appreciable separating force upon thewear plates.

The forces tending to separate wear plates 30, 30a from the gears arecounteracted by the rigid support of bushings =24, 24a by abutment face26. To counteract the forces tending to separate wear plates 32, 32afrom the gears, two fluid pressure operated pistons 42, 42a (FIG- URES 1and 3) are provided. They are respectively mounted in a pair of pistonchambers 43 and 43a formed in the end closure 12, and said pistons bearrespectively against the bearing blocks and 25a. The pistons 42 and 42aare spring-loaded at 44 to initially hold the bearing blocks, wearplates and gears in contact. During pump operation, however, thepressure of the delivered fluid in recess D and outlet 23 is appliedthrough second means or common passages 50, 51, including branchpassages 52, and 54, to the chamber 43 to the motive surface or outerface of piston 42 and through common passages 50, 51, and branchpassages 53, 55 to chamber 43a and piston 42a to cause the pistons to sopress against the bearing blocks 25 and 25a as to counteract theseparating force which the delivered fluid exerts on the wear plates. Asthis separating pressure is concentrated toward the delivery side of thepump, due to the groove 4 36, the counteracting pressure exerted by thepistons 42 and 42a must be greatest at said delivery side. In order toattain this end, the axes A of the pistons 42 and 42a and their chambers43 and 43a are offset toward the delivery side of the pump from thecenters C as shown in FIGURE 3.

To prevent any accumulation of pressure which might interfere withseating of the bearing blocks 24 and 24a against the end closure 11, agroove 45 (FIGURES 1 and 2) is formed in the inner side of said endclosure 11 and said groove is placed in communication with the fluidreceiving zone R by means of registering passages 46, 47 in said endclosure and the body 10 respectively. An O-ring seal 48 is providedaround the meeting ends of the pass-ages 46, 47. The blind passage 46ain FIGURE 2 comes into operation only when the body It) is turned withinthe closure caps 11 and 12 from the position shown for the purpose ofreversing pump rotation. It then registers with the passage 47. AnO-ring seal 49 is provided around the outer end of the passage 46a.

The force tending to separate the wear plates from the gear side facesfluctuates as the gears rotate. This is brought about by the fact thatthe wear plate area exposed to high pressure fluid within tooth pocketareas and in grooves 36 opposite gear tooth side faces fluctuates as thegears rotate. Thus for example, as gear 38 rotates in a counterclockwisedirection as viewed in FIG- URE 3, tooth 38b when in the full lineposition shown covers the end edge 36a of groove 36 and there is highpressure fluid in all the tooth pocket areas to the left of tooth 33b upto and including the tooth pocket area to the left of tooth 380, or sixtooth pocket areas in all. Thus, the gear 38 defines with the side facethereof and the wear plate 32 a plurality of tooth pocket areas forminga substantial peripheral area subject to increasing and decreasingfluctuating fluid pressure. At the same instant, seven teeth, from 38bto 38c are opposite groove 36. Thus at this instant wear plate 32 isacted upon by fluid pressurized substantially to the pressure of thefluid in outlet zone D across an area equal to that defined byapproximately six tooth pocket areas and seven segments of groove 36opposite gear teeth. This exerts a definite force on wear plate 32tending to separate it from the adjacent gear side face.

As gear 38 rotates counterclockwise slightly further so that tooth 38bmoves to the position shown in dotted lines in FIGURE 3, the end 3601 ofgroove 36 opens suddenly into the tooth pocket to the right of tooth 38band almost instantaneously pressurizes the fluid therein. This suddenlyadds the area of another tooth pocket to the area of wear plate 32subject to high pressure fluid and thus suddenly increases the totalforce acting on wear plate 32 tending to separate it from the gear sideface. It has been found that this sudden increase will actually move thewear plate against the holding force applied by piston 42 so as to causeleakage, unless special provision is made to prevent this eflect. Thisis particularly true when the area of piston 42 is so selected as tonormally apply a relatively small amount of overbalancing force forkeeping wear plate 32 in engagement with the gear side face withoutexcessively high contact pressure therebetween. 1

To prevent such sudden increase in the force tending to move wear plate32 away from the gear, provision is made for trapping the fluid behindpistons 42 and 42a in the respective chambers 43 and 43a. Since liquidis relatively incompressible, the trapped fluid acts as a solid abutmentto prevent such outward movement of the wear plates. Thus check valve 58prevents any substantial back flow from chamber 43 to outlet recess Dand check valve 58a prevents such back flow from chamber 43a. As asudden increase of force occurs on the inner face of either wear plate32, 32a, a very slight outward movement of the wear plate will occurwhich is transmitted by the respective bushing 25, 25a to thecorresponding piston 42, 42a and cause a rapid rise in pressure of thetrapped fluid in the pressure chamber to resist further outward motionof the parts. The outward motion of the wear plates for producing thispressure rise is so slight that it does not affect the seal against thegear side faces. This outward motion is checked and reversed by thesudden build up in pressure within chambers 43, 43a, and also by thegradual decrease of separating forces on wear plates 32, 32a.

Again considering Wear plate 32 and gear 38, as tooth 38b moves from thedotted position toward the position occupied by gear tooth 38d, therewill be no new tooth pocket exposed to pressure in groove 36 until tooth38e reaches the dotted position shown for tooth 38b. Thus at this regionof the gear, with each angular motion of the gear through an arc equalto the angular spacing between gear teeth centers, there will be asudden increase in area on the wear plate exposed to high pressure equalto the area of one gear tooth pocket area followed by a gradual decreaseof such exposed area to the extent of the area of one tooth pocket. Fromthis it is evident that there will be one cycle of sudden increase andgradual decrease in exposed wear plate area for every tooth pocket inthe gear during each complete revolution of the gear.

Meanwhile, at the meshing zone of the two gears, the tooth pocket areato the left of tooth 38c has all its area exposed to wear plate 32except for a very small portion blocked out by the tip of tooth 38f. Asgear 38 continues to rotate counterclockwise tooth 38] blocks morean'dmore of this tooth pocket area exposed to wear plate 32 until only avery small pocket area 38g, remains exposed to the wear plate and thefluid therein exerts high pressure onto the wear plate until the pocketpasses over center of the median plane P. Also, an increasing portion ofeach tooth pocket of gear 38 moves out of register with wear plate 32 asthe pocket passes median plane P. Thus it will be seen that at themeshing zone each tooth pocket gradually is reduced in its area ofexposure to the wear plate and there is no substantial sudden increasein area. Force fluctuations on the inner side of the wear plate are thusdue primarily to the cyclical increase and decrease in area of highpressure tooth pocket exposure in the vicinity of tooth 38b as alreadydescribed.

It will be noted that gear 38a is at all times angularly displaced onehalf the angular distance between tooth centers from the position ofgear 38, this being due to the gears being as shown in FIGURE 3 where itis about to suddenly expose the tooth pocket to the right thereof tohigh pressure in groove 36, tooth 38h is relatively one half a toothspacing farther onto the corresponding groove 36 and thus gear 38a is atabout the midpoint of its cycle for increasing and decreasing the areaof exposure to high pressure. As a result, the cycles for this effectfor the two gears are out of phase, the high point of one being at aboutthe midpoint of the other. To obtain most eflicient counteraction to theforce fluctuations, pressure chambers 43 and 43a are pressurizedindependently of each other and through individual check valves 58, 58a.Otherwise, if chambers 43, 43a are interconnected or are connected tothe outlet zone D through a common check-valve the volume of trappedfluid for resisting separation movement of the wear plates from thegears is doubled and hence the slight separating movement of each wearplate for compressing the fluid to build up the counteracting pressurewill be approximately doubled and thus result in less eflicient sealmg.

Each check valve 58, 58a is normally seated on a seat 57 by a lightspring 60 abutting a closure plug 56 for bores 53. The light springs 60permit the check valves to unseat readily for filling pressure chambers43 and 43a with fluid from outlet zone D when the pump is put intooperation.

Bleed holes 59 are provided in the check valves to permit delayedbalancing of pressures between each pressure chamber 43, 43a and theoutlet zone D when the pressure in either pressure chamber tends to rise(as by thermal expansion) or tends to remain (as when pump pressuredrops) higher than the pressure in the outlet zone. The bleed ports 59are of such size that they will not pass an appreciable amount of fluidduring the cycles of increasing and decreasing force on the wear platesdue to changing areas of tooth pocket exposure and thus do notappreciably effect the counteraction provided by the trapped fluid inthe pressure chambers 43, 43a. However, if the pressures in thesechambers start to rise above the pressure in outlet zone D due tothermal expansion, a small amount of fluid will bleed through the port59 from the chamber toward the outlet zone until the pressures aresubstantially balanced, that is, until the lowest pressure in thechamber during the cycles of fluctuating pressures therein issubstantially the same as in the outlet zone D.

Likewise, if the pump has been operating at one high pressure 2500p.s.i. for example (this being the pressure in outlet zone D), and iscut back to a lower pressure, such as 1000, p.s.i., the bleed ports 59will permit the pressure in the pressure chambers 43, 43a tocorrespondingly drop. Without the bleed port the higher pressure wouldbe maintained in the pressure chambers resulting in excessive force onthe wear plates for counteracting the pressure exerted on the inner sideof the wear plates tending to separate the wear plates from the gearswhich in turn would lead to excessive friction between the wear platesand gears with consequent excessive heating and loss of mechanicalefiiciency.

Packings 64 and 64a seal pistons 42, 42a so as to completely sealpressure chambers 43, 43a whereby all fluid entering or leaving thechambers must pass through check valves 58 and for bleed ports 59. Thispermits a highly accurate control of pressure and flow conditions forthe chambers and their relation to the separating force fluctuations.Thus, it is important to have relatively large passageways 50, 51, 52,53, 54 and 55 to permit rapid filling of the pressure chambers 43, 43awhen starting the pump. The bleed ports 59 must be small enough topermit no appreciable loss of fluid from the chambers during theseparating force fluctuation cycles when the pressure within thechambers rises from substantially pump discharge pressure to a higherpressure and recedes again to discharge pressure. On the other hand, thebleed ports must be large enough to bleed excess pressure from thechambers, due to causes noted above, whenever the pressure in thechambers remains at a value higher than pump discharge pressure for aperiod of time longer than the cycle time for the fluctuating separatingforces. It has been found, for example, that for a gear pump designed tooperate at pressures up to 25,000 p.s.i. and speeds up to 2500 rpm, withten teeth per gear, minimum and maximum areas of 4.38 and 5.13 squareinches of wear surface exposed to high pressure, and with a piston areaof 5.93 square inches, a .007" diameter for bleed ports 59 providesexcellent results. From this it is apparent that it is important thatleakproof packings 64, 64a be provided. Otherwise, leakage from thechambers 43, 43a past the pistons 42, 42a which would be very diflicultto control precisely with normal machining practices and dimensionaltolerances, would make it impossible to achieve effective sealing of thewear plates without a substantial overbalance of pressure thereagainstwith resulting poor mechanical efiiciency.

I claim:

1. A fluid pressure translating device comprising a housing, a chamberin said housing, an inlet recess leading to and an outlet recess leadingfrom said chamber, a rotary member in said chamber subject to fluidunder pressure, said member having a. surface to be sealed, a movableelement in engagement with said surface for sealing the same, saidmovable element defining with said surface a plurality of areas forminga substantially peripheral area extending from said outlet recess to aposition in close proximity to said inlet recess with alternating areasthereof subject to fluid under pressure tending to separate the movableelement from said surface, first means subjecting said entiresubstantially peripheral area to increasing and decreasing fluidpressure fluctuating forces as said rotary member rotates, said firstmeans providing pressure communication between said chamber and saidoutlet recess, at least one of said areas which is otherwise closed tothe oulet recess being in communication with said outlet recess throughsaid first means, second means in communication solely with said firstmeans and said outlet recess for applying second forces to said movableelement in opposition to said separating'forces whereby said element ismaintained in sealing contact with said surface, and third means incommunication only with said second means and said movable element forsolely causing said second forces to increasingly and decreasinglyfluctuate substantially in phase, duration and in like manner with saidfirst forces and maintain a substantially uniform incremental forcedifferential therebetween irrespective .of whether the said first forcesare increasing or decreasing.

2. A fluid pressure translating device in accordance with claim 1wherein said first means includes a groove cooperative with said rotarymember to produce said fluid pressure fluctuating forces as said rotarymember rotates.

13. A fluid pressure translating device in accordance with claim .1wherein said third means includes a valve means for causing said secondforces to fluctuate. v

4. A fluid pressure translating device in accordance with claim 1wherein said first means includes a groove cooperative with saidrotarymember to produce said fluid pressure fluctuating forces as saidrotary member rotates, and said third means includes valve means forcausing said second forces to fluctuate.

S. -A fluid pressure translating device in accordance with claim 4including a piston chamber within said housing, a piston in said pistonchamber cooperative with said movable element and said valve means forapplying said second forces to said movable element in opposition tosaid first forces for maintaining said movable element in sealingengagement with said surface.

*6. A fluid pressure translating device in accordance with claim 5:where said second means is a passage for conducting fluid underpressure from said out-let recess to said piston chamber, said valvemeans including a bleed port connecting said passage to said recess forpermitting a delayed balancing of said fluid fluctuating forces by saidsecond forces.

7. A fluid pressure translating device in accordance with claim 4including a pair of piston chambers within said housing, a piston ineach of said piston chambers cooperative with said movable element andsaid valve means for applying said second forces to said movable elementin opposition to said first forces for maintaining said movable elementin sealing engagement with said surface.

8. A fluid pressure translating device comprising a housing, a chamberin said housing, an inlet recess leading to and an outlet recess leadingfrom said chamber, a pair of rotary members in said chamber subject tofluid under pressure, said rotary members each having a surface to besealed, a movable element in engagement with each of said surfaces forsealing the same, said movable element defining with said surface aplurality of pocket areas forming a pair of substantially peripheralareas extending from said outlet recess to a position in close proximityto said inlet recess with alternating pocket areas thereof subject tofluid under pressure tending to separate the movable element from saidsurface, a pair of grooves,

each of said grooves subjecting one of said pair of periphtuating forcesas said pair of rotary members rotate, said grooves providing pressurecommunication between said chamber and said outlet recess, at least oneof said pocket areas of each of said pair of peripheral areas which isotherwise closed to the outlet recess being in communication with saidoutlet recess through the groove of each of said pair of grooves, apassage in communication solely with said grooves and said outlet recessfor applying second forces to said movable element in opposition to saidseparating forces whereby said elements are maintained in sealingcontact with each of said surfaces, and valve means in communicationonly with said passage and said movable elements for solely causing saidsecond forces to increasingly and decreasingly fluctuate substantiallyin phase, duration and in like manner with said first forces andmaintain a substantially uniform incremental force differentialtherebetween irrespective of whether the said first forces areincreasing or decreasing. 9. A fluid pressure translating device inaccordance with claim 8 wherein said housing includes a pair of pistonchambers and said passage includes a pair of branch passages incommunication with each of said piston chamers, a piston within each ofsaid piston chambers cooperative with said movable element, and saidvalve means includes an individual check valve in each of said branchpassages for applying said second forces individually to each of saidpistons in opposition to said first forces for maintaining said movableelements in sealing engagement with said surfaces.

10. A fluid pressure translating device in accordance with claim 9wherein said movable elements are wear plates and each of said checkvalves includes a bleed port for permitting a delayed balancing of saidfluid fluctuating forces by said second forces.

11. A fluid pressure translating device comprising a housing, a chamberin said housing, an inlet recess leading to and an outlet recess leadingfrom said chamber, a rotary member in said chamber subject to fluidunder pressure, said member having a surface to be sealed, a movableelement in engagement with said surface for sealing the same, saidmovable element defining with said surface a plurality of areas forminga substantially peripheral area extending from said outlet recess to aposition in close proximity to said inlet recess with alternating areasthereof subject to fluid under pressure tending to separate the movableelement from said surface, first means subjecting said entiresubstantially peripheral area to increasing and decreasing fluidpressure fluctuating forces as said rotary member rotates, said firstmeans providing pressure communication between said chamber and saidoutlet recess, at least one of said areas which is otherwise closed tothe outlet recess being in communication with said outlet recess throughsaid first means, second means for applying second forces to saidmovabie element in opposition to said separating forces whereby saidelement is maintained in sealing contact with said surface, and thirdmeans in communication with said second means and said movable elementfor causing said second forces to increasingly and decreasinglyfluctuate in like manner with said first forces and maintain a substantially uniform incremental force differential therebetweenirrespective of whether the said first forces are increasing ordecreasing.

ing to and an outlet recess leading from said chamber,

a rotary member in said chamber subject to fluid under pressure, saidmember having a surface to be sealed, a

movable element in engagement with said surface for sealing the same,said movable element defining with said surface a plurality of areasforming a substantially peripheral area extending from said outletrecess to a position in close proximity to said inlet recess withalternating areas thereof subject to fluid under pressure tending toseparate the movable element from said surface,

first means subjecting said entire substantially peripheral area toincreasing and decreasing fluid pressure fluctuating forces as saidrotary member rotates, said first means providing pressure communicationbetween said chamber and said outlet recess, at least one of said areaswhich is otherwise closed to the outlet recess being in communicationwith said outlet recess through said first means, second means incommunication with said first means and said outlet recess for applyingsecond forces to said movable element in opposition to said separatingforces whereby said element is maintained in sealing contact with saidsurface, and third means in communication with said second means andsaid movable element for causing said second forces to increasingly anddecreasingly fluctuate substantially in phase, duration and in likemanner with said first forces and maintain a substantially uniformincremental force differential therebetween irrespective of whether thesaid first forces are increasing or decreasing.

13. A gear pump comprising a housing, a chamber in the housing, an inletrecess leading to and an outlet recess leading from said chamber, a pairof meshed rotary gears in the housing for delivering fluid from saidinlet recess to said outlet recess, a bushing for each gear and incontact with the side face thereof for sealing the same, a fluidpressure actuated piston in contact with each bushing for urging thesame into sealing contact with the gear side face, passage means leadingfrom the outlet recess to one side of the piston for at all timesconducting fluid from said outlet recess against said piston, and acheck valve in said passage means for permitting flow of fluid from saidoutlet recess to said one side of said piston, and a restricted passageof predetermined flow capacity for permitting flow of fluid from saidone side of said piston to said outlet recess.

14. The gear pump of claim 13 in which said restricted passage is insaid check valve.

15. The gear pump of claim 13 including means in the gear side facecooperating with said gears for communicating increasing and decreasingfluctuating forces to said passage means whereby said pistons movesubstantially in phase, duration and in like manners with thefluctuating forces.

16. A fluid pressure translating device comprising a housing, a pair ofchambers in said housing, an inlet recess leading to and an outletrecess leading from said chambers, a rotary member in each of saidchambers subject to fluid under pressure, each of said members having asurface to be sealed, a movable element in engagement with each of saidsurfaces, means for counteracting the fluid pressure acting to separatethe movable elements and the rotary members to maintain the movableelements in engagement with said surfaces, said counteracting meansincluding a pair of fluid pressure operating pistons, each piston beingmounted in a piston chamber, spring means for urging each piston towardan associated one of said movable elements, passage means opening intosaid outlet recess, branch passage means between said passage means andeach of said piston chambers for communicating outlet fluid pressureinto each piston chamber, individual valve means between said passagemeans .and said branch passage means for independently pressurizing thepiston chambers, each of said valve means being a check valve, saidbranch passages each including a seat receiving a check valve, a springurging each check valve upon its associated seat, and a bleed passage ineach check valve.

17. The fluid pressure translating device of claim 16 wherein saidmovable elements each comprise a generally circular plate having acentral opening, an arcuate groove in a surface of said plate concentricwith said opening, a short groove in said surface between said arcuategroove and opening through a peripheral edge portion of the plate, andsaid peripheral edge portion including a notch adjacent said shortgroove.

18. The fluid pressure translating device of claim 17 wherein saidarcuate groove has opposite end portions spaced from each othersubstantially 180 degrees, and said short groove is positioned adjacentone of said end portions.

References Cited by the Examiner UNITED STATES PATENTS 2,420,622 5/47Roth et al 103126 2,624,287 1/53= llyin 103126 2,772,638 12/56 Nagely103-216 2,816,512 12/57 Murray 103126 2,865,302 12/58 Murray 103'1262,870,719 1/59 Murray et a1. l03126 2,924,182 2/ Blasutta et al. 1032162,974,605 3/61 Murray 103-126 FOREIGN PATENTS 706,979 4/54 GreatBritain.

KARL J. ALBRECHT, Primary Examiner.

WIDBUR J. GOODLIN, JOSEPH H. BRANSON, JR., Examiners.

1. A FLUID PRESSURE TRANSLATING DEIVCE COMPRISING A HOUSING, A CHAMBERIN SAID HOUSING, AN INLET RECCESS LEADING TO AND AN OUTLET RECESSLEADING FROM SAID CHAMBER, A ROTARY MEMBER IN SAID CHAMBER SUBJECT TOFLUID UNDER PRESSURE, SAID MEMBER HAVING SURFACCE TO BE SEALED, AMOVABLE ELEMENT IN ENGAGEMENT WITH SAID SURFACE FOR MOVABLE ELEMENT INENGAGEMENT WITH SAID SURFACE FOR SURFACE A PLURALITY OF AREAS FORMING ASUBSTANTIALLY PERIPHERAL AREA EXTENNDING FROM SAID OUTLET RECESS TO APOSITIONN IN CLOSE PROXIMITY TO SAID INLET RECCESS WITH ALTERNATINGAREAS THEREOF SUBJECT TO FLUID UNDER PRESSURE TENDING TO SEPARATE THEMOVABLE ELEMENT FROM SAID SURFACE, FIRST MEANS SUBJECTING SAID ENTIRESUBSTANTIALLY PERIIPHERAL AREA TO INCREASING AND DECREASING FLUIDPRESDURE FLUCTUATING FORCES AS SAID ROTARY MEMBER ROTATES, SAID FIRSTMEANS PROVIIDING PRKESSURE COMMUNICATION BETWEEN SAID CHAMBER AND SAIDOUTLET RECESS, AT LEAST ONE OF SAID AREAS WHICH IS OTHERWISE CLOSED TOTHE OUTLET RECESS BEING IN COMMUNICATION WITH SAID OUTTLET RECESSTHROUGH SAID FIRST MEANS, SECOND MEANS IN COMMUNICATION SOLELY WITH SAIDFIRSTT MEANS AND SAID OUTLET RECESS FOR APPLYING SECOND FORCES TO SAIDMOVEABLE ELEMENT IN OPPOSITION TO SAID SEPARRATING FORCES WHEREBY SAIDELEMENT IS MAINTAINED IN SEALING CONTCT WITHH SAID SURFACCE, AND THIRDMEANS IN COMMUNICATION ONLY WITHH SAIDD SECOND MEANS AND SAID MOVABLEELEMENT FOR SOLELY CAUSING SAID SECOND FORCES TO INCREASINGLY ANDDECREASINGLYY FLUCTUATE SUBSTANTIALLY IN PHASE, DURATION AND IN LIKEMANNER WITH SAID FIRST FORCES AND MAINTAIN A SUBSTANTIALLY UNIFORMINCREMENTAL FORCE DIFFERENTIAL THEREBETWEEN IRRESPECTIVE OF WHETHER THESAID FFIRIST FORCES ARE INCREASING OR DECREASING.